This invention relates generally to cardiac rhythm management systems and particularly, to a cardiac rhythm management system with an electrosurgery mode.
When functioning properly, the human heart maintains its own intrinsic rhythm, and is capable of pumping adequate blood throughout the body""s circulatory system. However, some people have irregular cardiac rhythms, referred to as cardiac arrhythmias. Such arrhythmias result in diminished blood circulation. One mode of treating cardiac arrhythmias is via drug therapy. Drugs are often effective at restoring normal heart rhythms. However, drug therapy is not always effective for treating arrhythmias of certain patients. For such patients, an alternative mode of treatment is needed. One such alternative mode of treatment includes the use of a cardiac rhythm management system. Such systems are often implanted in the patient and deliver therapy to the heart.
Cardiac rhythm management systems include, among other things, pacemakers, also referred to as pacers. Pacers deliver timed sequences of low energy electrical stimuli, called pace pulses, to the heart, such as via a transvenous leadwire having one or more electrodes disposed in the heart. Heart contractions are initiated in response to such pace pulses. By properly timing the delivery of pace pulses, the heart can be induced to contract in proper rhythm, greatly improving its efficiency as a pump. Pacers are often used to treat patients with bradyarrhythmias, that is, hearts that beat too slowly, or irregularly.
Cardiac rhythm management systems also include cardioverters or defibrillators that are capable of delivering higher energy electrical stimuli to the heart. Defibrillators are often used to treat patients with tachyarrhythmias, that is, hearts that beat too quickly. Such too-fast heart rhythms also cause diminished blood circulation because the heart isn""t allowed sufficient time to fill with blood before contracting to expel the blood. Such pumping by the heart is inefficient. A defibrillator is capable of delivering an high energy electrical stimulus that is sometimes referred to as a countershock. The countershock interrupts the tachyarrhythmia, allowing the heart to reestablish a normal rhythm for the efficient pumping of blood. In addition to pacers, cardiac rhythm management systems also include, among other things, pacer/defibrillators that combine the functions of pacers and defibrillators, drug delivery devices, and any other systems or devices for diagnosing or treating cardiac arrhythmias.
One problem that arises in implantable cardiac rhythm management devices is possible adverse consequences to such devices when a physician is performing electrosurgery on the patient in which the device is implanted. See Neil F. Strathmore, xe2x80x9cInterference in Cardiac Pacemakers,xe2x80x9d (Kenneth A. Ellenbogen, G. Neal Kay, and Bruce L. Wilkoff, eds. xe2x80x9cClinical Cardiac Pacing,xe2x80x9d 1st ed., pp. 772-73 (1995)). Electrosurgery includes electrocautery, diathermy, and radio-frequency (RF) ablation. Electrosurgery uses electromagnetic energy, such as RF currents, to cut, coagulate, and/or congeal the patient""s tissue. For example, RF ablation is used to modify the conduction paths of intrinsic heart signals through cardiac tissue in order to treat cardiac arrhythmias. There are many other applications of electrosurgery.
The RF signals used in performing electrosurgery may interfere with proper operation of the implanted cardiac rhythm management device, particularly if the electrosurgical electrodes are used near the implanted device. For example, circuits in the implanted device that sense intrinsic heart signals may interpret an RF electrosurgery signal as an intrinsic cardiac depolarization. In response, the implanted device may be inhibited from delivering a needed pacing pulse. In other implanted devices, the RF electrosurgery signals may cause the implanted device to revert to a backup/reset/startup mode of operation. The implanted cardiac rhythm management device will not return to normal operation until the implanted device is reprogrammed via an external programmer. This can cause hemodynamic compromise if the backup parameters are inadequate for the particular patient in which the cardiac rhythm management device is implanted.
Some implanted devices may be vulnerable to reprogramming by the RF electrosurgery signal itself when a magnet is applied during the electrosurgery procedure to ensure asynchronous pacing (i.e., ignoring sensed intrinsic heart signals) during the electrosurgery procedure. Such reprogramming by the RF electrosurgery signal may leave the patient without adequate cardiac rhythm management therapy, or may even result in the delivery of inappropriate therapy by the RF-reprogrammed implanted device. Thus, there is a need to reduce the risk of adverse interactions between an implanted cardiac rhythm management device and an electrosurgical instrument being used on a patient in which the device is implanted.
The present system provides a cardiac rhythm management system including an implantable cardiac rhythm management device having an electrosurgery state, also referred to as an electrosurgery mode. The electrosurgery mode programs certain device parameters to particular electrosurgery mode values in order to increase the immunity of the implanted device to interference resulting from the electrosurgery. Some of the electrosurgery mode device parameter values use corresponding previously programmed values from a normal mode of operation. Others of the electrosurgery mode device parameter values may be different from the corresponding previously programmed values from the normal mode of operation.
The present cardiac rhythm management system allows a user to use an external programmer to initiate an electrosurgery mode in an implanted cardiac rhythm management device, where the device parameter values used in the electrosurgery mode are both safe for use during electrosurgery and provide effective therapy to the patient, at least insofar as certain of the previously programmed device parameters were tailored for providing effective therapy to the patient.
In one embodiment, the cardiac rhythm management (CRM) system includes an external programmer and an implantable CRM device. The CRM device includes an electrosurgery state initiated by a first command received from the external programmer. Initiation of the electrosurgery state results in a request for confirmation from the user of the external programmer, identification of the electrosurgery state to the user of the external programmer, and the disabling of further programming of bradyarrhythmia and tachyarrhythmia parameters until the electrosurgery state is exited by a second command received from the external programmer. During the electrosurgery state both bradyarrhythmia and tachyarrhythmia mode device parameters are programmed to particular values corresponding to electrosurgery mode. The device is configured to deliver asynchronous pacing (e.g., pacing mode set to DOO, AOO, VOO, etc.). In one example, a pacing mode is set to DOO, providing atrial and ventricular pacing, deactivating sensing of atrial and ventricular intrinsic heart signals, and providing no pacing therapy in response to the atrial and ventricular intrinsic heart signals. A pacing rate, a fixed atrial-ventricular (AV) delay, atrial and ventricular pacing amplitudes, and atrial and ventricular pacing pulse widths are each set to a corresponding value programmed prior to initiation of the electrosurgery state. Tachyarrhythmia sensing and therapy are disabled. Aspects of the present cardiac rhythm management system, including its electrosurgery mode, are presented in the following detailed description of the invention and the corresponding drawings that form a part thereof.